My corolla, VE model, 75K mileage has cold start problem. Mechanic says, I need to replace TPS (Throttle Positesion sensor) and Oxygen sensor. Also cleanup fuel injector. It does not start first time in the morning and sometimes in evening. Engine check sign also comes (sometimes, and disappear at times). Any sugestions??

He may be right. We would know more if you had the codes read. That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code not just their translation into English and post it back here.

If your mechanic came to this conclusion by reading the trouble codes in the computer, he is probably correct. I don’t agree with the fuel injector cleaning, however, as it’s usually nothing more than a profit generator.

Further suggestions are: to change the spark plugs and wires, air filter, and pcv valve. Then, check the strength of spark on all plugs. If weak spark(s) suspect (check) the ignition coil. If the spark plugs show a rich condition (black, or sooty), check the engine coolant temperature sensor (Or, as a shortcut to checking, change the sensor).